Closed-Loop Antenna Selection for Wireless LANs with Directional & Omni-Directional Elements

Throughput and packet error rate are analysed in a home environment for two different 3×3 wireless LAN solutions. A 3×3 EBF approach (using three radio chains) is compared with a reduced cost 2×2 architecture (using two radio chains). In the 2×2 solution the optimum antenna pair is selected from the same set of three antennas at the AP and client. The impact of directional, as well as omni- directional, antenna elements is considered. The spatial and temporal characteristics of the in-home channels are modelled using 3D ray tracing and combined with appropriately orientated complex polarmetric patterns for each antenna element. Physical layer throughput is calculated for all modulation and coding schemes and (for the 2×2 case) all possible antenna combinations using a novel received bit mutual information rate abstraction technique. Results show that antenna number, pattern and orientation all play a key role in determining the performance of an 802.11n system. As expected, 3×3 EBF outperforms the 2×2 solution; however, with optimum antenna selection the performance of 2×2 EBF is competitive, especially when directional antennas are used at low signal to noise ratios. For distant rooms, 3×3 EBF is only 15% better (in terms of throughput) than 2×2 EBF when directional antennas and dynamic antenna selection are applied. 2×2 EBF with omni antennas results in a 45% reduction in throughput (compared with 3×3 EBF).